Currently diamonds are widely used in various industries such as aerospace, semiconductor, precision machinery, optical instrument, automotive, composite materials, etc.
A leading trend, influencing the entire industrial diamond field, is the growing use of the so-called nanodiamonds or Ultra Disperse Diamonds (UDD) or Ultra NanoCrystalline Diamonds (UNCD), which are the boundary state of a substance between individual molecules and a bulk state of a material. Nanodiamond powder is currently the most innovative synthetic diamond type which was discovered in Russia in the mid-60s and has been applied presently in various technologies due to its unique features enabling creation new composite materials and objects with desired properties.
Currently nanodiamond is widely used as the additive to polymer compounds, lubricants and coatings, as abrasive in fine polishing compositions, in catalysts and advanced composite materials, as well as in biological and nano-medical research for various applications.
The process of nanodiamond manufacturing usually includes two main stages: synthesis and purification.
Currently several techniques exist for nanodiamond synthesis. Nanodiamond is usually synthesized from carbon contained in molecules of explosives by the detonating (called nanodiamond of detonation origin). Nanodiamond could be also synthesized from a suspension of graphite in organic liquid at atmospheric pressure and room temperature using ultrasonic cavitations. The yield is approximately 10%. An alternative synthesis technique is irradiation of graphite by high-energy laser pulses. The structure and particle size of the obtained diamond is rather similar to that obtained in explosion.
Generally, the nanodiamond explosive synthesis is performed by the detonation of solid explosives in inert atmosphere from carbon source contained in explosive molecules (see, for example, V. Yu. Dolmatov, “Detonation synthesis of ultra-dispersed diamonds: properties and applications” Russian Chemical Reviews, 2001, V. 7(7), P, 607-626). In the front of detonation wave chemical bond splitting occurs causing instantaneous liberation of enormous amounts of energy. Under high temperatures (3000-4000 K.) and pressures (20-30 GPa) high-dispersed carbon medium is condensed from explosive carbon in a fraction of a microsecond. Conditions of detonation synthesis do not provide complete conversion of explosive carbon into a diamond phase. Carbon yield is 4-10% of an explosive weight, and significant purification and isolation steps are required.
The nanodiamond purification of UDD synthesized by detonation of solid explosives is a complex process that includes various mechanical and chemical treatments. In particular, the nanodiamonds purification usually starts from mechanical removal of various admixtures created during the process of preparation. Thereafter, in order to separate the diamond phase, the diamond—carbonic powder is subjected to thermal oxidation with compositions containing sulfuric and nitric acids. Then, after separation from acidic media, the nanodiamond grains are rinsed with water.
For example, PCT Application No. WO 03/086970 to Korjenevsky et al. describes a technique for the production and purification of ultra dispersed synthetic diamonds. The method involves the detonation-transformation of explosive material having a negative oxygen balance in the closed space of a blasting chamber in a nonoxidizing atmosphere, the evacuation of explosion products and the heat chemical purification thereof by a mineral acid followed by washing of impurities therefrom. The condensed detonation products are additionally exposed to the action of a shock wave. The chemical purification is carried out with a nitrogen acid aqueous solution in three stages: in the first stage, in periodic mode at a temperature ranging from 20 to 60° C.° during the time of 0.5 to 5 hours; in the second stage, in continuous mode and in five temperature zones at a temperature ranging from 110 to 300° C.° during the time of 20 to 120 minutes; and in the third stage, in periodic mode at a temperature ranging from 20 to 80° C.° during the time of 0.5 to 5 hours with the additional blowing of a reaction mass by an oxygen—containing gas mixture. The additional action of the shock wave on the condensed products is carried out repeatedly from 1 to 50 times at intervals ranging from 5 to 20 minutes, the pressure of a front shock being specified within the range of 0.4 to 15.0 MPA.
A method of production of ultra-dispersed diamond without providing an inert gas environment is described in U.S. Pat. No. 5,353,708 to Stavrev et al. The process comprises the steps of exploding, in a confined space, an organic explosive surrounded by water, wherein the organic explosive has a stoichiometrically negative oxygen balance, which explosion is initiated, in a normal environment or in a low-vacuum environment. The detonation process proceeds in an explosively unrelieved, confined space. The explosives are located in a solid shell, e.g. autoclave with radial axial control of the detonation process from the center of the charge to its periphery, and in a soft shell with radial-axial control from the periphery of the charge to its center. A typical charge is from about 400 grams to about 800 grams for a cylindrical space of about 1.2 meters diameter by 1.8 meters length The nanodiamonds produced by prior art detonation methods, depending on the conditions of the detonation synthesis, are characterized by a relatively broad variance of particle sizes typically ranging between 2 and 50 nm. The primary nanodiamond particles form fractal cluster structures (of 30-40 nm size) which consequently form larger aggregates (of an order of magnitude of hundreds of nanometers). In their usual state, the nanodiamonds produced by the prior art technique represent a powder that may have the purity of up to about 96-98% by weight of UDD particles, the volume of pores in the range of 0.3-1.1 nm3/gram, the average diameter of the pores in the range of 8-10 nm.
A non-explosive method for synthesizing nanodiamond crystals continuously at normal temperature and normal pressure is described in Chinese Patent No. 1547843 to Wengong Zhang, et al. According to this method, the surface of solid carbon source present in a continuously flowing (and shifting) soaking liquid phase, is impacted with focused pulse laser beam under the protection of proper protective atmosphere. The thickness of the liquid thin layer overflowing the surface of solid carbon source was controlling to be in the range of 0.01 to 5.00 mm with a liquid flow rate between 0.002 and 0.500 ml/sec. As a result, nanodiamond particles are formed in the high temperature and high pressure micro-area created in the solid-liquid interface before flowing out of the processing area (reactor).
General Description
The present invention, according to its one broad aspect, provides a new approach for the producing nanodiamonds, based on the creating acoustic shock-waves by radiation beam focused in the transparent liquid at the some predetermined distance from the surface of the specially prepared solid target containing carbon non-diamond source. Treating the specially prepared target by the acoustic shock waves leads to the forming of diamond nanocrystals.
In some embodiments of the invention the process of nanodiamond synthesis could be controlled by varying at least one of the distance between the focusing plane and the surface of the solid carbon source target and/or energy flux and/or width and/or shape of the laser pulse and/or content of the specially prepared carbon source target. For example average primary particle size from 3.9 to 300 nm could be controlled by varying at least energy intensity of the radiation beam.
By using this method, nanodiamond having, improved properties (purity, uniformity, etc.) could be prepared.
According to another broad aspect of the present invention there is provided a method of synthesizing powder of nanodiamond comprising;                providing a carbon source target;        providing a layer of liquid on the surface of the carbon source target;        generating an irradiation energy beam;        focusing said irradiation energy beam or beams onto a selected area located within the liquid and at a predetermined distance above the surface of the carbon source target.        
The certain hydrodynamic effect is created impacting surface of carbon source target and more specifically providing conditions (e.g. temperature, pressure, etc.) sufficient for forming diamond cubic crystal structure. Such so called “light-hydraulic effect” was discovered and disclosed in 1963 year as “Science Discovery” registered in the USSR under number No. 65 in the name of A. Prokhorov et al.
Providing liquid layer on the surface of carbon source target could be performed by immersing the target into the liquid.
The present invention, in yet further aspect, may provide further cleaning or purification of the synthesized nanodiamond material. Nanodiamonds could be isolation and cleaned by flotation method in de-ionized water with further optional washing and drying.
The carbon containing material of target could include at least one element selected from fullerene, amorphous carbon, graphite, solid hydrocarbons.
The liquid may comprise at least water, glycerin, acetone, benzene or another liquid hydrocarbon.
The irradiation energy beam(s) may be produced by a laser.
In some embodiments, the laser being operated at least one wavelength within the range of 532 to 1320 nm.
The irradiation energy beam may be produced by at least one laser pulse.
In some embodiments, the laser pulse is a rectangular pulse.
A laser pulse width may be in the range of 1 nanosecond to about 5000 nanoseconds and most preferably of 10 to about 20 nanoseconds.
Laser pulse intensity may be in the range of about 106 to about 1013 W/cm2 and preferably of about 1010 to about 1011 W/cm2.
The predetermined distance above the surface of the carbon source target may be in the range of about 0.1 to about 20 mm and preferably may be about 2-3 mm.
According to another broad aspect of the invention, there is provided a system for nanodiamond synthesis comprising:
a holding assembly for accommodating a carbon containing carbon source target immersed in a liquid, an irradiation energy assembly configured for producing an irradiation energy beam, directed towards the carbon source target and focused onto a selected area located within the liquid at a predetermined distance and above surface of said carbon source target.
Holding assembly could include a liquid containing vessel for accommodation of carbon source target immersed in liquid.
In some embodiments, the vessel may include a window transparent to the irradiation energy beam passing there through.
The irradiation energy source may include a laser operable to emit light at least one wavelength in the range from 532 to 1320 nm and preferably 1064 nm.
According to another broad aspect of the invention an ultra dispersed diamond composition of matter is provided characterized by at least one of the following parameters:
i) having a purity of more than 99%;
ii) having an average particle size between 3.9 to 300 nanometers.
Preferably, in accordance with the present invention the nanodiamond composition of matter has all the above characteristics, i.e. has a purity of more than 99% and a particle distribution between 2 and 30 nm.
Preferably, the purity is more than 99%, preferably above 99.6% and most preferably above 99.9%.
Nanodiamond particle size distribution may be between 2 and 20 nm, or between 2 and 12 nm, or between 2 and 8 nm and most preferably between 2 and 4 nm.
The term “nanodiamond composition of matter” means a final form (product) in which the nanodiamond is presented to the consumer; including not only nanodiamond particles, but also a small amount of impurities in the composition of matter (mixture) which are residuals of carbon source target material, or other, e.g. environment material used in the process.
In accordance with one aspect of the present invention the nanodiamond composition of matter could predominantly (more than 99.6%, and preferably 99.95%) be composed of nanodiamond particles themselves,
The purity of the nanodiamond powder produced by the method and system of the present invention can be up to 99.96 wt. % that superior the competitive figure of about 98 wt. % of the prior art nanodiamond product. Likewise, the nanodiamond powder according to the present invention is characterized by a narrow size distribution of the nanodiamond particles, e.g. mainly about of 4-5 nm.
The nanodiamond product according to the present invention may be easily and efficiently manufactured without the need for expensive equipment, reaction mixtures or lengthy and complicated purification processes.
The nanodiamond product according to the present invention may have a low manufacturing cost.
Various preparations could be produced based on the nanodiamond of the present invention, such as polishing products, lubricants, coolants, pharmaceutical preparations; polymer composites, chemical caring preparation, electro-static spraying preparation, additive in electrolytes, precursor preparation for the diamond growth by CVD method, catalyst preparation, etc.